This invention relates to material flow control devices for production system for producing plural species of works or articles, by which the operation rates of the production devices within the production system are stabilized and are not susceptible to disturbing factors such as the occurrence of a failure of the production devices.
FIG. 8 is a block diagram showing the functional structure of a conventional material flow control device. The material flow control device controls a plurality of controlled production units of a production system as shown in FIG. 10, using a waiting queue file shown in FIG. 9.
The amounts of works (the parts or articles which are produced in the production system) engaged in respective controlled units within the production system are measured by an engagement amount measuring unit 101. The processing order determination unit 102 determines the order of the processing of the works on the basis of the first-in first-out (FIFO) principle as described below. The status of the production system is input via a production system status input unit 103 to trigger the material flow control, and the processing instructions are output from a processing instruction output unit 104 to the respective controlled units within the production system.
FIG. 10 is a block diagram showing the simplified structural model of the conventional production system. The production system includes a plurality of controlled production equipment units 601 through 603. The order of the processing is determined by a material flow control device 604 whose structure is shown in FIG. 8. The controlled unit 603, for example, includes a plurality of production device groups 605 and 606.
FIG. 9 is a diagram showing a processing wait queue for a production unit 603 within the production system of FIG. 10 controlled by the material flow control device of FIG. 8. The waiting queue file or processing wait accumulation file 800 is generated within the processing order determination unit 102. A plurality of processing waiting request items 801 through 805 are accumulated in a waiting queue file 800. The leading numerals within the elongated circles represent respective sources of the processing requests, and the numerals after the hyphen represent the generation order of the requests. The numbers at the right of respective encircled items represent the order of processing of the works in the controlled unit 603. Thus, the requests with the leading number 601 within the circle represent works which are to be transferred from the controlled unit 601 to the controlled unit 603. On the other hand, the requests with the leading number 602 represent works which are to be transferred from controlled unit 602 to controlled unit 603. As shown in the figure, the order of processing is determined by the simple first-in first-out (FIFO) principle, without regard to the source unit or the destination device group of the requests.
Next, the operation of the conventional material flow control device is described. It is assumed that the works are transferred from the material flow control units 601 and 602 to the controlled unit 603. Then, the requests for processing the works originating from the controlled unit 601 and those originating from the controlled unit 602 are detected by the engagement amount measuring unit 101, and are accumulated in the waiting queue file 800 within the processing order determination unit 102.
When the controlled unit 603 is ready for accepting further works, it outputs its ready status to the production system status input unit 103. Upon receiving this status signal from the controlled unit 603, the production system status input unit 103 supplies a flow control trigger signal to the processing order determination unit 102. In response thereto, the processing order determination unit 102 outputs via the processing instruction output unit 104 the processing instruction for the bottom request item (the oldest request) in the waiting queue file 800. The processing instruction is output to the controlled unit 601 or controlled unit 602 in accordance with the indication of the source in the processed item in the waiting queue file 800. As a result, the works either in the controlled unit 601 or the controlled unit 602 are dispensed and transferred to the device group 605 or the device group 606 within the controlled unit 603. The processing order is determined simply by the first-in first-out (FIFO) principle, without regard to the source (controlled unit 601 or controlled unit 602) or the destination (device group 605 or device group 606) of the request.
Thus, the above conventional material flow control device has the following disadvantage. Assume that the device group 605 within the controlled unit 603 is occupied in processing the works while the device group 606 is in an idle state (not occupied). Further assume that the oldest processing request within the waiting queue file 800 is destined for the device group 605. Then, the works are first dispensed from the controlled unit 601 and transferred to the device group 605 in spite of the fact that the device group 605 is busy and the device group 606 is idle. As a result, the device group 606 remains idle and the working rate thereof is reduced.
Further, assume that the device group 605 undergoes a failure, and that the older request items in the waiting queue file 800 are destined for the device group 605. Then, the works destined for the device group 605 are first dispensed, and if the failure of the device group 605 continues, the engagement amount of the works therefor increases continuously. The distribution of the amounts of engaged works within the whole production system thus becomes uneven, and the operation rates of the respective device groups 605 and 606 become uneven.